1. Field of the Invention
The present invention, in general, relates to batteries and, more particularly, to charging lead acid batteries.
Battery chargers are well known devices used for automotive, commercial, marine, aviation, and military applications to restore an electrical charge to a dead or weak battery.
Lead acid storage batteries are the most common of these types of batteries and it is a 12-volt lead acid type of battery that is described herein for use with the instant invention. However, the instant invention is applicable for use with any type and voltage of a battery that can benefit from the improvement methods as herein disclosed.
With many applications, such as automotive, a battery is typically held near or at its maximum energy capacity by the charging system of the vehicle. When power is drawn from the battery, for example to start the vehicle, it is soon replenished by the vehicle's charging system. This is an ideal operating environment for a battery and maximum battery life-expectancy is usually realized.
However, there are many situations in which a battery is not used for a protracted period of time, or if used, is not recharged. This is especially hard on lead acid types of batteries.
In some cases the batteries are initially charged to capacity but are then left for weeks or months without being used or serviced. The battery naturally loses its charge (i.e., its reserve and starting capacity) by self-discharge from the local action of impurities of the lead plates and interaction with the electrolyte.
This self-discharge is accelerated at elevated temperatures, and will eventually result in a drop in the terminal voltage of the battery, especially below 1.75 volts per cell (10.5V total for a 12V battery).
Once this threshold is reached, and the battery is left for as little as 24 hours without recharge, it results in lead sulfate particles crystallizing on surfaces of the positive and negative plates. These lead sulfate crystals form a high electrical-resistance that is difficult to remove from the battery plates. This tendency is generally well known and is also discussed in U.S. Navy T.O. 8DZ-62-1. The term “sulfate”, as generally used herein, refers to this process or activity, whereas the term “sulfated”, as generally used herein, refers to a battery that is affected by and is manifesting this condition.
This crystallized lead sulfate coating substantially increases the internal impedance of the battery. This, in turn, prevents normal battery function from occurring. The battery is no longer capable of delivering sufficient power to a load. Similarly, the high internal impedance affects the ability of the battery to be re-charged.
When a battery charger is connected to a “sulfated” battery, the high internal impedance prohibits re-charging of the battery. The battery charger can remain connected for hours, even days or weeks to no avail. The battery simply will not accept charge current.
In some cases the sulfated battery may gradually begin to accept a charge and be restored but in the vast majority of cases a conventional type of prior art battery charger cannot penetrate the high-impedance sulfated layering that has been deposited on the lead plates of the battery sufficient to dislodge the sulfurous materials or compounds (which are derived from the sulfuric acid) and restore them once again properly back into the electrolyte which includes sulfuric acid. Prior art battery chargers that are used in an attempt to “desulfate”, or return the battery to a usable state, are sometimes effective only after very long periods of time after connection. This can often be weeks.
Sulfated batteries that have been in storage or out of use for an extended period of time are generally regarded as useless and most are discarded as hazardous waste while a lesser amount are recycled. This causes tremendous negative environmental impact and enormous financial cost.
There are other causes that contribute to the formation of lead sulfate crystals. Another common cause contributing to the rapid formation of the crystallized lead sulfate coating is by storing a highly discharged battery for even a relatively short period of time, such as 3-4 days, without recharge when an electrical load is also connected to the battery. This is a common problem when lights or other loads are left on batteries for protracted periods of time.
As with self-discharge, high temperatures can further accelerate the sulfating problem. In either case the high resistance crystallized lead sulfate coating eventually results in a “dead” battery with high internal impedance that can not typically be recharged. The sulfated battery may still present some voltage at the battery terminals, but because of the high internal resistance it cannot supply anywhere near a normal current draw, and is therefore considered as dead regardless of whether there is any voltage present at the terminals.
The content of the related patent application that is identified at the beginning of this application is included herein by way of reference, and it provides an improved battery charger and method for restoring or charging batteries that greatly improves efficacy when attempting to restore to usefulness and charge a sulfated battery.
However, there are some batteries that are so severely sulfated or which may also suffer from other defects which, as a result, cannot be restored to usefulness regardless of how much time or effort is expended. These “hopeless” types of batteries cannot be restored or charged to usefulness either by conventional prior art battery chargers or prior art battery charging methods or by the technology and methods as disclosed in the related patent application.
Fortunately, there are relatively few of the hopeless types of batteries. However, there has before been no effective way of determining which of those batteries that are sulfated are hopeless apart from those that are restorable to usefulness other than by investing a great deal of time in vain attempting to restore and charge such a battery and then eventually, deeming the battery as hopeless.
Accordingly, prior determinations that a sulfated battery is hopeless have been done by subjective and arbitrary means, primarily involving the investment of a variable amount of time for restoration and charging of the battery and resulting in the abandonment of the effort and discard of the battery upon the battery failing to be restored and accept a charge in the allocated amount of time. The amount of time is variable because it varies from place to place and person to person. The amount of time for attempting to charge a sulfated battery is determined for the most part by the patience of the person attempting to restore the sulfated battery and in accordance with any governing procedures or suggestions that may exist or be applicable.
It is desirable to be able to make such a determination accurately and as quickly as possible so as to avoid wasted time when attempting to charge a hopeless battery for an extended period of time and also to avoid discarding other batteries that are wrongly deemed as being hopeless when they can, in fact, be restored.
Also, batteries generally build up heat when being charged regardless of the type of charger because, if any current is flowing through the battery, energy (power) is being dissipated in the battery and some of that energy appears as heat. In particular, the use of the technologies as disclosed in the related patent application rely on very high energy pulses to restore lead acid batteries by an internal heating and the breaking up of even high grade (III) sulfation.
With sealed types of batteries, this heat has few ways to escape from the battery, other than by thermodynamic conduction through the battery case and battery terminals. Accordingly, a rise in the temperature at the terminals is experienced and can be detected. Excessive heat can damage the battery if the battery rises in temperature to a typical range of from 45 to 50 degrees Celsius, or more. Additionally, very high battery temperatures can cause an out-gassing of potentially explosive hydrogen gas and pose a risk to those that are nearby.
It is desirable to determine if, during charging, an internal temperature of a battery exceeds a predetermined threshold temperature and if this occurs to either lessen the rate of charge or terminate the attempted charge, as desired.
If the battery being charged has not been determined to be hopeless, it is desirable to lessen the rate of charge rather than terminate the entire charging process if the predetermined threshold temperature is exceeded. For some situations, it may be preferable to lessen the rate of charge to a low value and then increase the rate of charge after the battery has cooled to an acceptable temperature for batteries that are still deemed to have hope of recovery. For other situations with batteries that are still deemed to have hope of recovery it may be preferable to lessen the rate of charge to zero (to temporarily stop charging) and then resume some rate of charging after the battery has cooled to an acceptable temperature.
Either of these responses will extend the overall amount of time that is being used to attempt recovery of the battery. For a hopeless battery it is desirable to cease the restoration and charging attempt as soon as possible. Ideally, for a battery it is desirable to determine if the battery is hopeless and if it is so determined to cease the restoration attempt before a battery experiences a rise in temperature that exceeds the predetermined threshold temperature.
If a battery can be determined to be hopeless at approximately the same time as when the battery experiences a rise in temperature that exceeds the predetermined threshold temperature, it is desirable to terminate the restoration effort and to not resume the effort after the battery has cooled. To resume the restoration effort would only waste time and resources.
Ideally, it is preferable to be able to determine whether or not a battery can be restored to usefulness and if it is determined that the battery is hopeless and cannot be restored to usefulness to terminate the restoration effort as quickly as possible. However, if it has not been determined that the battery is hopeless, it is desirable to resume the restoration effort for a battery that has exceeded a predetermined threshold temperature after the battery has cooled.
It is desirable to provide an indication, either visual or otherwise, for any battery that is determined to be hopeless as accurately and as quickly as possible. This capability could be used by an operator to either continue or cease the restoration effort. It is even more desirable to include as much determination capability and decision making capability as part of the charging equipment so as to better automate the restoration and charging process and to lessen the need for operator presence and operator decision making during restoration and charging, thereby even further lessening labor expenses and the cost of restoration and charging sulfated batteries.
Accordingly, there exists today a need for a method and apparatus for using a battery terminal temperature differential during charging of the battery that helps to ameliorate the above-mentioned problems and difficulties as well as ameliorate those additional problems and difficulties as may be recited in the “OBJECTS AND SUMMARY OF THE INVENTION” or discussed elsewhere in the specification or which may otherwise exist or occur and that are not specifically mentioned herein.
Clearly, such a method would be useful and the apparatus would be a desirable device.
2. Description of Prior Art
Battery chargers are, in general, known. While the structural arrangements of the above described and known prior art devices may, at first appearance, have certain similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior art devices.